Chest pain (angina pectoris) is a cardinal symptom of coronary artery disease. However, not all patients with myocardial ischemia have chest pain and not all patients with angina-like chest pain have coronary artery disease or myocardial ischemia. Mechanisms of angina pectoris are complex and not fully understood because limited information exists about the central neural pathways and mechanisms mediating cardiac pain in man. The purpose of this study is to evaluate the role of central nervous system (CNS) endogenous opiate systems involved in producing cardiac chest pain. F-18 cyclofoxy (6-deoxy-6-fluoronaltrexone), a positron emitting opiate receptor antagonist, is being used for quantification of CNS endogenous opiate receptors in man. At the time of dictation, two patients have been studied. Preliminary data analysis is ongoing. The plan is to continue subject accrual and data analysis.